A radiant heating system is composed of tubing embedded in flooring, walls, or ceilings of the area to be heated. Heated water is pumped through this tubing to raise the temperature of the surface (thermal mass). Heat energy radiating from the thermal mass heats the objects in the room. As the method of heat transfer in these systems is primarily radiant, lower temperature water is required to heat the thermal mass than is typically needed for convection type systems (e.g., finned tube baseboard heating). In systems where the heat source is not solely dedicated to supplying heated water to the radiant loop, a means of tempering the higher temperature water from a heating unit loop, or other type of heating unit loop, is necessary to maintain lower temperature requirements in the radiant loop. An injection loop can perform this tempering by supplying water from the heating unit loop to the radiant loop. The amount of heated water injected into the radiant loop can be set using a manually adjusted mixing valve, or using a variable speed injection pump. Alternatively, if the heating unit is a domestic hot water heater, and water from the heating unit loop may be used as potable water, the water in the heating unit loop may be isolated from the water in the radiant loop and heat may be transferred from the heating unit loop to the radiant loop via a heat exchanger.
FIG. 1 shows a prior art hydronic system of the type described above. There are two independent circulator pumps: a circulator pump 12 circulating water from the water heater 10 through the heating unit loop, and a radiant loop circulator pump 16 for circulating water through the radiant loop and thereby the coils 18 of the radiant heating system. The water in the two loops flows through two sides of a heat exchanger 14, in the directions indicated by the arrows in FIG. 1, causing heat to transfer from the water entering the heating unit loop from the outlet of the water heater, to the water returning from the radiant loop. A thermostat 19 and associated electrical circuit controls a relay 20 that switches the two circulators on.
This type of heat-exchanger-based water circulating system may also be used with other types of heat sources, e.g., a boiler, in applications in which it is desirable to separate the water in the two loops. For instance, if an antifreeze solution is used in the radiant loop, e.g., for an outdoor heated driveway or walkway, it may be desirable to isolate the water in the heating unit loop from the antifreeze solution even if the heat source is a boiler or other source that does not supply potable water.
The circulator pumps are typically of the wet rotor circulator type. The pump impeller is received in a mating cavity known as a volute. Typically, the volute is surrounded by a flange to which the pump is attached. When the pump is installed, and the impeller thereby positioned within the volute, water enters the pump through an inlet at the center of the volute, and exits through an outlet in the periphery of the volute.